1. Field of the Invention
The present invention relates to a magnetic head for recording/reproducing information to and from a magnetic recording medium, and more particularly, to a magnetic head adapted to a large coercive force medium for use in video tape recorders (VTR) or digital audio tape recorders (DAT).
2. Description of the Related Art
A fact has been well known that it is advantageous for a high density magnetic recording/reproducing apparatus to enlarge the coercive force (Hc) of a magnetic recording medium for use therein. Accordingly, a ferrous alloy powder tape, the Hc of which is 1200 to 1500 oersted (Oe), has been used in VTRs recently. In order to record/reproduce a signal to/from a high Hc tape of the type described above, JP-A-58-155513 and JP-A-60-32107 each proposed using magnetic heads with a metal magnetic material of a highly saturated flux density such as Fe-Si-Al (Sendust alloy) and an amorphous Co-Nb-Zr alloy.
In particular, the width of the recording track to be recorded on the magnetic recording medium has been reduced with the recent desire of raising the density of magnetic recording. Accordingly, there arises a desire of significantly reducing the track width of the magnetic head.
Therefore, composite type magnetic heads have been proposed in JP-A-62-138110 and JP-A-62-157306 each of which is arranged in such a manner that magnetic cores are made of a ferromagnetic oxide such as ferrite, and that a ferromagnetic metal film is applied to the surface regions of the magnetic cores between which a magnetic gap is formed.
The above-described magnetic head is, as shown in FIG. 15, constituted in such a manner that abutment surfaces of a pair of magnetic cores 101 and 102 are respectively diagonally cut off, with the magnetic cores 101 and 102 being made of ferromagnetic oxide such as Mn-Zn ferrite. The surfaces 103 and 104 are formed before ferromagnetic metal films 105 and 106 made of, for example, an Fe-Al-Si alloy (Sendust alloy) are applied to the surfaces of thus formed diagonal surfaces 103 and 104 by a vacuum process of forming thin film. The end edge surfaces of the ferromagnetic metal films 105 and 106 are disposed in opposition to each other so that a magnetic gap 107 is formed. Furthermore, low melting point glass materials 108 and 109 or high melting point glass materials 110 and 111 are filled in a track width restricting groove formed by the abutment of the cores 101 and 102 against each other in order to prevent wear.
An example of a method of manufacturing the conventional composite type magnetic head will now be described with reference to the drawings in accordance with its sequential order.
As shown in FIGS. 16A and 16B, a plurality of parallel cut grooves 121, each of which has a substantially V-shaped cross section, are formed on the upper surface side 120a of an oxide magnetic substrate 120 made of, for example, Mn-Zn ferrite, using a rotary grindstone. That is, the parallel grooves 121 are formed on the overall width of the joining surface of the substrate 120 for making magnetic core half bodies abut against each other. As a result, surfaces 121a, on which a thin magnetic film is formed, are formed.
Then, as shown in FIG. 17, an Fe-Al-Si alloy or an amorphous alloy coating is applied to the entire surface of the top surface 120a of the substrate 120 including the surfaces 121a by utilizing a vacuum thin film forming process such as a sputtering process so that a thin magnetic metal film 122 is formed on the substrate 120.
Subsequently, a nonmagnetic material 123 is filled in the V-shaped grooves 121 to which the film 122 is applied. Then, the top surface 120a, with the film 122, of the substrate 120 is ground to be flat so that a desired surface exhibiting an excellent smoothness is formed (see FIGS. 18A and 18B). Furthermore, end edge surfaces 122a of the magnetic film 122 appear on the top surface of the substrate 120.
Then, as shown in FIGS. 19A and 19B, second cut grooves 124 having substantially circular-arc shaped cross sections are, in parallel to the first cut grooves 121, formed by cutting in the portions adjacent to the surfaces 121a on which the magnetic film 122 is applied. In a case where the thickness of the magnetic metal film 122 is substantially the same as the track width Tw, the second cut grooves 124 having the substantially circular-arc shaped cross sections are formed by cutting so as to reach the end edge portions of the film 122 (see FIG. 19B).
Furthermore, a groove 125 is formed on a magnetic core block 140 which is a component of a pair consisting of magnetic core blocks 130 and 140 manufactured by the above-described process, the groove (coil winding groove) 125 being formed perpendicularly to the first and second cut grooves 121 and 124 as shown in FIG. 20, which is one for winding a coil wire in a final product.
Then, coatings as gap spacers are effected on joining surfaces 130a of the magnetic core block 130. Furthermore, the blocks 130 and 140 are coupled to each other in such a manner that the end edge surfaces 122a of the films 122 abut against one another. The blocks 130 and 140 are, then, coupled to each other by using molten glass and nonmagnetic material is filled within each of the second cut grooves 124.
Finally, a plurality of head chips are obtained by slicing, as designated by lines A--A and A'--A' in FIG. 21, before the surface, with which a magnetic tape comes
i in contact, is ground to form a cylindrical shape. As a result, a plurality of magnetic head cores 150 are produced (see FIGS. 22 and 23).
The magnetic head shown in FIG. 15 is produced in such a manner that a process of forming the first grooves in the substrate made of, for example, the ferromagnetic oxide, is performed so that inclined surfaces, which correspond to the thin ferromagnetic film formed surfaces, are formed. Next, the thin ferromagnetic metal film is formed on the inclined surfaces before it is ground to form a flat surface. Then, each of the second grooves is formed so that a desired track width is established by depending upon the accuracy of the position of the second groove.
However, the above-described method encounters a problem in that the accuracy of the track width become excessively non-uniform because it depends upon the pitch accuracy of the first grooves, that of the second grooves and the accuracy in the manufacturing processes arranged to be performed to the grinding process. For example, the variation of the first groove positions is about 5 to 7 .mu.m, that of the thickness of the ferromagnetic metal film is about 2 to 4 .mu.m and that of the second grooves is about 2 to 3 .mu.m. Therefore, it is difficult to realize the allowable total variation of the track width of .+-.1 .mu.m or .+-.2 .mu.m between each of the final products of the magnetic heads. Furthermore, in a case of a narrow track smaller than 20 .mu.m, a strict accuracy is required in the operation of abutting a pair of magnetic cores such that each of magnetic gaps is formed.
Another problem resides in that a satisfactory manufacturing yield cannot be obtained due to the generation of bubbles in the two processes in each of which glass is filled and due to the too complicated manufacturing process. Furthermore, since a multiplicity of materials are employed to form the magnetic head, an non-uniform wear takes place in the surface with which a magnetic tape comes in contact. As a result, the characteristics of the magnetic head will deteriorate.
On the other hand, it has been known that composite type magnetic heads of the above-described type (which are magnetic heads arranged in such a manner that the magnetic cores are made of a ferromagnetic oxide such as ferrite and a ferromagnetic metal film is applied to the surface region of each of the magnetic cores in which the magnetic gap is formed) and also disclosed in JP-A-62-138110 and JP-A-62-157306 exhibit an advantage in that noise generation due to the contact with a magnetic tape can be relatively reduced in comparison to a magnetic head made of only ferromagnetic oxide. However, the composite type magnetic head involves a problem in that noise caused from the ferromagnetic oxide cannot be satisfactorily reduced because its cores made of ferromagnetic oxide come in contact with a magnetic tape.